The present invention relates to a chemical-mechanical polishing (CMP) slurry recycling apparatus for recycling a CMP slurry and a method for recycling a CMP slurry, which are adapted to enable a decrease in costs incurred in chemically-mechanically polishing semiconductor wafers and other objects by repetitive use of a CMP slurry.
A CMP process is used in planarizing the surfaces of wafers, substrates and other objects before subjecting e.g. semiconductor wafers to exposure processing. The CMP process is a polishing process that combines a chemical reaction by a solute in a slurry as a polishing fluid and a mechanical polishing action produced by a polishing pad and abrasive particles in the slurry.
In conventional CMP processes, a slurry is not reused and is discarded. As polishing slurry is expensive, discarding it after a single use contributes to the expense of producing semi-conductor wafers.
The slurry is collected in a storage tank, and then discarded. Collection of used slurry is effected by means of a collecting trough disposed so as to enclose an outer peripheral surface of a polishing table and a bottom portion thereof. The slurry supplied to the polishing pad is allowed to flow from the polishing pad along the outer peripheral surface of the polishing table and the bottom portion thereof into the collecting trough, and the slurry flown into the collecting trough is then transferred to the storage tank for withdrawal of the slurry. In such a conventional polishing process, the used slurry comes into contact with a wide area of the outer peripheral surface and the bottom surface of the polishing table before it is collected in the collecting trough. This extensive contact of the used slurry with the polishing table gives rise to a risk of a portion of the slurry sticking to and becoming solid on the outer peripheral surface of the polishing table or the bottom surface when the slurry is flown from the polishing pad to the collecting trough. Further, there is a risk of the slurry scattering from the rotating polishing table and not reaching the collection trough. Attempts have so far been made to recycle and reuse slurry deposited in a storage tank. It has been found necessary, however, for fresh slurry to be supplemented in a large amount in order to efficiently reuse the slurry once used, because efficiency of collecting the used slurry is very low.
Therefore, the present invention has the object to provide a CMP slurry recycling apparatus and a method for recycling a CMP slurry once used, which enables costs in a planarizing process for planarizing the surfaces of semiconductor wafers and other objects to be reduced by reusing and recycling the used CMP slurry in an efficient way.
In order to achieve the object in one aspect, the present invention provides a CMP slurry recycling apparatus for recycling a CMN slurry, in which the slurry is supplied to a polishing pad disposed on a polishing table to polish the polishing object, while the used slurry is withdrawn from the polishing pad, wherein the polishing table is arranged such that a diameter thereof is set to be smaller relative to the diameter of the polishing pad and wherein a collecting device having an opening on top thereof is disposed around the outer peripheral surface of the polishing table so as to withdraw the slurry directly from the polishing pad in the device.
With the arrangement of the apparatus as described above, the CMP slurry recycling apparatus according to the present invention can increase efficiency in withdrawing the used CMP slurry by directly collecting or withdrawing the used slurry from the polishing pad because it can prevent the used slurry from sticking and becoming solid on the surfaces of the polishing table and from scattering from the polishing pad.
In a preferred embodiment of the present invention, the device is composed of a trough in a U-shaped transverse section and disposed around the outer periphery of the polishing table so as for a top end at an inner edge side of the trough to be located in a slightly spaced relationship below the outer peripheral bottom edge portion of the polishing pad.
In order to achieve the object in another aspect, the present invention provides the CMP slurry recycling method for recycling a CMP slurry, in which the slurry is supplied to a polishing pad disposed on a polishing table to polish the polishing object, while the used slurry is withdrawn from the polishing pad, the method comprising the steps of: setting a diameter of the polishing table to be smaller than a diameter of the polishing pad; arranging a generally U-shaped device having an opening on top thereof around the outer peripheral surface of the polishing table so as for a top edge of the device at the inner edge side thereof to be located under the outer peripheral bottom surface portion of the polishing pad; withdrawing the used slurry in the device directly from the peripheral edge of the polishing pad through the opening; transferring the used slurry withdrawn by the device to a storage tank after filtering to remove contaminants; and supplying the slurry from the storage tank to the polishing pad disposed on the polishing table after further filtering to remove contaminants.
Other objects, features and advantages of the present invention will become apparent in the course of the following description with reference to the accompanying drawings.